Python: filter more sinks in stdlib

Rename variable to reflect larger scope

We had test results inside `os.py`, I suppose we have found a little extra flow.

python/ql/lib/semmle/python/security/dataflow/PathInjectionCustomizations.qll

@@ -71,11 +71,11 @@ module PathInjection {
       // ```
       //
       // The same approach is used in the command injection query.
-      not exists(Module pathlib |
-        pathlib.getName() = "pathlib" and
-        this.getScope().getEnclosingModule() = pathlib and
-        // do allow this call if we're analyzing pathlib.py as part of CPython though
-        not exists(pathlib.getFile().getRelativePath())
+      not exists(Module inStdlib |
+        inStdlib.getName() in ["pathlib", "os"] and
+        this.getScope().getEnclosingModule() = inStdlib and
+        // do allow this call if we're analyzing, say, pathlib.py as part of CPython though
+        not exists(inStdlib.getFile().getRelativePath())
       )
     }
   }